<!DOCTYPE html>
<html lang="zh-CN">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    div {
      /* content(width height) */
      width: 100px;
      height: 100px;

      /* padding */
      padding: 100px;

      /* border */
      border: 1px solid black;

      /* margin */
      margin: 100px;

      background-color: rgba(17, 119, 255, 0.5);
    }
  </style>
</head>

<body>
  <div></div>
</body>

</html>